The present invention relates to a synchronous linear motor having a secondary part which is in the form of a toothed rod and has no permanent magnets, with the secondary part having a predetermined toothed structure in the movement direction of the synchronous linear motor.
A position signal for determination of the instantaneous commutation angle and/or for position control is required for controlled operation of a synchronous linear motor. This signal is generally obtained from an external position measurement system, which is independent of the active part of the motor. Other known solutions provide for the use of permanent magnets in the secondary part extent, as transmitters for the position signal. Hall sensors are frequently used to obtain signals for this purpose.
However, an external position measurement system is generally complex and is not practicable, or is practicable only with major technical complexity and high costs, in applications with a high degree of dirt or similar disturbances resulting from the working process of the machine. Furthermore, a measurement system with Hall sensors is relatively highly inaccurate for detection of permanent magnets of the secondary part for obtaining position signals, and is therefore only rarely suitable for position control. The reason for this is the mechanical and magnetic tolerances of the secondary part as the transmitter. Specifically, the tolerances in the magnet dimensions and magnetic characteristics of the individual magnets cause sinusoidal or cosinusoidal amplitude errors. Furthermore, position errors of the individual magnets on the secondary part extent cause graduation errors in the measurement system.
For the present document, it should be stressed that the movement of a synchronous linear motor is in principle a relative movement of any type between a primary part and secondary part of the motor even when, for example, all that is described is movement of the primary part over the secondary part. A similar situation applies to the positions of the primary part with respect to the secondary part.